How can I parent objects from different scenes?
I ran into a problem very much like this when I went to create fireworks. At the time, I assumed the same thing as you, "One must use BR for halo particles." I did not run into the camera problem because I used the Track To Object constraint for the cameras so that they would follow the firework's progress. I set the alpha to none and used the alpha over node in the compositor to combine the two scenes.

The assumption that one must use BR for halo particles, however, is not true.

Using the point density node as shown in this tutorial will allow you to use Cycles to render halo particles.



Alternately, to answer the question you asked...

Scenes

I used the default Blender startup file for my example, as it has a camera, light source, and object. The first thing I did is duplicate the scene by pressing New Scene -> Full Copy.

Animation

Go back to the original scene and insert a key frame at frame one, move the camera, and then insert one at a later frame. The camera should now move when you play the animation. Next, go to the Animation Screen Layout. Make sure the scene selected is not the one with the moving camera. Select the non-moving camera. Go to the Dope Sheet panel and change the type from Dope Sheet to Action Editor (the same way you would change from Object to Edit mode in the 3D View). Where it says + New along the bottom options, click on the dropdown menu to the left side, the same way you would select an old material rather than creating a new material. Somewhere in there should be something resembling CameraAction, or Camera.001Action (the name of the moving camera followed by Action). Click on this. The movement of the two cameras should now be linked.